Monday, July 31, 2023

Answer to Case 723

Answer to the Parasite Case of the Week 723: mite, not scabies. Given that this mite was found in a fungal culture from skin scrapings, it could very well be a dust mite (Dermatophagoides sp.) as many of you suggested. However, mites are challenging to identify, so genus/species level identification is best left to the acarologists (people who study mites and ticks). 

The biggest concern here is its location - on a fungal culture in the mycology laboratory. Mites are a terror in the mycology lab. They crawl from plate to plate, contaminating and destroying cultures from patient samples. In most cases, the culture plates need to be destroyed and the lab decontaminated. This is the reason why my colleague, Dr. Wengenack, was so upset to find these! However, she knew of my interest in mites and was kind enough to donate this case to the blog.

Some readers questioned if these were scabies mites. Fortunately scabies mites (Sarcoptes scabei) can be easily differentiated from most zoonotic and environmental mites by their rounded bodies and short legs:

Sunday, July 16, 2023

Case of the Week 722

 This week's (rather disturbing) case was generously donated by Dr. Niels Olson. This is a parasite found in salmon throughout the world - sorry sushi lovers - no slight is meant against any commercial provider of salmon. Parasitism is a fact of life. What is the likely identification of this parasite? What would happen if it was ingested without cooking or freezing?

Saturday, July 15, 2023

Answer to Case 722

Answer to the Parasite Case of the Week 722: anisakid larvae, one of the members of the Anisakis simplex, Pseudoterranova decipiens, or Contracecum osculatum complex. 

Humans can become transiently infected with the larvae when they are ingested in undercooked fish, such as this salmon. The larvae may embed in the gastric or intestinal mucosa, causing intense pain. Endoscopic removal is curative. In less severe cases, the larvae will migrate back up the esophagus and out the mouth - a much preferred (but disturbing!) alternative. They can also be passed in the stool. In these settings, the larvae have to be differentiated from immature Ascaris lumbricoides. This can be accomplished using a number of morphologic features. 

To avoid anisakiasis, Chia-Yu Chiu wisely notes that the FDA recommends that salmon (and all fish) should be well-cooked or frozen prior to ingesting to kill the larvae.  This case is a good example of how fish is not always frozen prior to sale - even in a well known grocery chain. Therefore, it is up to the consumer to freeze the fish prior to eating raw! The FDA recommends freezing for 7 days using a standard, consumer-grade freezer (-20℃). Restaurants usually freeze for 24 hours or less at -70℃. 

On a final note, some people develop an allergy to anisakids, and therefore even freezing won't protect from allergic reactions following consumption. Individuals with severe anisakid allergies may have to avoid ocean fish indefinitely.

Tuesday, July 4, 2023

Case of the Week 721

 Happy American Independence day (July 4th) and a belated Canada day (July 1st)! As an American, this weeks case very appropriately has a lot of red, white, and (purple-ish)
blue. The following round objects were seen in a stool specimen on modified acid fast. The patient has had more than 1 week of profuse watery diarrhea and abdominal discomfort.

These objects were also highlighted with using calcofluor white fluorescence staining (arrow) along with stool flora.

What are these objects? Are they fungus or parasite?

Monday, July 3, 2023

Answer to Case 721

 Answer to the Parasite Case of the Week 721: Cryptosporidium sp. oocysts. These oocysts are a parasite, even though they stain with the non-specific calcofluor white fluorescent dye. Also, the abbreviation "crypto" is often used to refer to either Cryptosporidium (parasite) or Cryptococcus (fungus), so it's always good to make sure you audience know what you were talking about!

Cryptosporidium spp. oocysts are one of several intestinal parasites that stain red with the modified acid fast stain; Cyclospora spp. and Cystoisospora belli are the other two. Note that these 3 parasite genera are commonly referred to as coccidian parasites (i.e., member of teh Coccidia group). However, evidence now indicates that Cryptosporidium more closely related to the Gregarinasina group. I've purposely shown these 3 organisms in my last 3 cases for comparison. Here is a composite image of the 3 parasites together:

Thanks again to Dr. Nazia Nagi for donating the C. belli case.